Disposable absorbent garments such as disposable diapers and adult incontinence briefs have met with widespread use to absorb and contain body exudates. Commercially available disposable diapers, for example, are unitary preshaped and prefolded garments which include a moisture-impervious backing sheet, a body contacting layer or liner and a moisture absorbent core therebetween. Elasticized leg openings are formed at the sides of the diaper and elasticized front and back waist sections are formed at the ends of the diaper to improve the comfort of the garment and its ability to contain waste material.
One step in the process for forming disposable garments such as disposable diapers involves the attachment of strips of elastic material at longitudinally spaced locations along a moving sheet or web of the polyethylene material which forms the backing sheet of the disposable garment. Currently, an endless strip of elastic material is unwound from a roll and moved in a direction transverse to the path of a moving sheet of the polyethylene material. An adhesive dispenser applies one or two extruded beads, or a continuous coating, of hot melt thermoplastic adhesive to the elastic material which is then moved from the adhesive dispenser to a cutting station where it is cut lengthwise to form individual strips. These individual strips of elastic material are then attached at longitudinally spaced locations along the moving polyethylene material which form the front and back waist sections of the finished disposable garment. After the elastic strips are attached to the polyethylene backing sheet, further process steps are employed to attach the other layers of the diaper to form the finished garment.
In most methods, the elastic material utilized to form the waist elastic member of the disposable garment is a heat shrinkable material, which, under the application of sufficient heat, shrinks or shortens in length. Because this heat shrinkable elastic material is secured to the polyethylene backing sheet of the disposable garment, it forms gathers or pleats in the polyethylene material upon shrinkage. These gathers improve the fit of the garment on the wearer and aid in resisting the passage of body exudates out of the garment.
A number of problems have been encountered in the method described above for attaching heat shrinkable elastic material at the waist portions of disposable garments. As mentioned above, the elastic material utilized in such application is heat shrinkable so that gathers can be formed at the waist portions of the finished garment. It has been found that the application of relatively thick, extruded beads of adhesive or a continuous coating of adhesive onto this heat shrinkable elastic material can cause such material to prematurely activate or shrink. This is because thick extruded beads or a continuous coating of hot melt thermoplastic adhesive retain substantial specific heat after discharge from a dispensing device and upon application onto the heat shrinkable elastic material. As a result, a number of chill rollers must be employed downstream from the adhesive dispensers to reduce the temperature of the hot melt adhesive applied to the heat shrinkable elastic material and thus prevent such elastic material from activating or shrinking prematurely.
Another problem with the method described above is that the adhesive dispensers which apply hot melt adhesive to the heat shrinkable elastic material generally employ slot nozzles which contact the elastic material to obtain an adhesive pattern thereon which is uniform and sharply defined at the edges of the individual strips. This contact between the elastic material and slot nozzles tends to wear the slot nozzles requiring frequent replacement. Additionally, a mechanism must be provided to retract the nozzle from its contact position with the elastic material when the manufacturing operation is interrupted or terminated.
A further disadvantage of the method described above is that a relatively large quantity of adhesive is discharged in the form of extruded beads or a continuous coating from the adhesive dispensers utilized in such method. Moreover, the hot melt thermoplastic adhesive is highly viscous and can dull or clog the knife blades utilized to cut the elastic material to length in preparation for its attachment to the polyethylene backing sheet of the diaper. This leads to maintenance problems wherein the knife blades must either be replaced or cleaned of adhesive in order for the diaper manufacturing operation to proceed.